Dimerization of conjugated dienes



gal-v United tate nt reaction rates as well as improved yields of the desired dimer and reduced formation of troublesome polymer.

2 974 176 It is an object of this invention to provide an improved I a process for the dimerization of conjugated dienes. It DIMERIZATION 0F CONJUGATED DIENES 5 is another object of this invention to provide a method for selectively dimerizing conjugated dienes having from 4 6 Company a corporation of Delaware to provide a method of d1mer1zmg 1,3-butadiene to form vinylcyclohexene with increased reactionrates and re- No' Drawing. Filed Aug. 5, 1957, Ser. No. 676,434 1o duced polymer formation. Other objects, advantages, j and features of our invention will be readily apparent to 7 Claims ago-"666) those skilled in the art from the following description and the appendant claims. While our invention is directed particularly to the This invention relates to an improved process for diformation of y y y dimefizing merizing conjugated dienes. In another aspect this inbutadiene, it is applicable also to the selective dimeriza-- vention relates to a process for the selective formation tion of similar conjugated dienes known to be subject to of dimers of conjugated dienes having from 4 to 6 carbon thermal dimerization reactions to form cyclic compounds. atoms per molecule. In one of its more specific aspects Examples of such conjugated dienes, in addition to 1,3- this invention relates to an improved process for the probutadiene, r isoprene, Piperylene and conjugated dienes duction of vinylcyclohexene by dimerizing 1,3-butadiene. having 6 carbon atoms per molecule, for example di- Conjugated dienes such as 1,3-butadiene, isoprene, propenyl and diisopropenyl. Mixtures of these conpiperylene and the like can be polymerized thermally withjugated dienes can also be reacted to form cyclic codimers. out the benefit of catalysts. By properly controlling re- The diluent which is employed according to the process action conditions it is possible to selectively dimerize these of our invention is normally a mixture of paraflinic hyconjugated dienes and reduce the amount of trimer, drocarbons which are highly branched although a single tetramer and higher polymer formed in the reaction. branched-chain paraffin having a boiling point in the These dimers can be depolymerized and are'therefore a range specified would be also suitable. The diluent to convenient formof storage or shipping the monomer. In be employed is substantially free of aromatics. The addition, the dimer is itself a valuable intermediate in preferred hydrocarbon mixtures have a minimum initial chemical reactions such as in polymerization to form boiling point of about 335 F. and a maximum end boildrying oils, resins, or rubbery polymers. While selective ing point of about 500 F. In the manufacture of vinyldimerization has been achieved with substantial success cyclohexene, we prefer to use as a diluent a branchedby control of reaction conditions the formation of polychain paraflin mixture boiling in the lower portion of mer has nevertheless been a consistent problem in comthis range, that is, having an initial boiling point of at mercial applications of this reaction. least about 335 F. and a maximum end boilingpoint of We have now discovered that lowerconjugated dienes about 410 F. For thebenefit of further describing this can be selectively dimerized with improved yields and rediluent the following data is set forth which shows the duced polymer formation by employing as a diluent a typical properties of four commercially available special branched-chain parafiinic hydrocarbon or mixture of purpose hydrocarbon products of this type which are such hydrocarbons which are substantially odorless and commonly known as odorless thinners. For purposes free of aromatics and which boil in the range of 270 to of reference in this specification these solvents are des- 800 F., preferably in the range of about 335 to 500 ignated as diluents A, B, C and D. It should be under- F. We have found that this particular type of diluent, stood that the following properties are typical only and which is formed commercially as a product of HF alkylav should not be interpreted to limit unduly the identification of isobutane and butylenes, is unexpectedly superior tion of the hydrocarbon diluent which is employed in to solvents previously employed as diluents in this rethe practice of our invention.

Typical Properties Dlluent Dlluent Diluent Diluent Test Methods A B o D InltialBolling Polut,F 349 354 424 399 ASTM D86-52. End boiling point, F 406 440 463 480 ASTM D86-52. Refractive index at20 1.4217 1. 4237 1. 4315 1.435 Bromlnenumber 0. 0. 1. 1.0 ASTM D1159-52. Kaurl-Butanol value, ml 25.3 24.0 23.4 726.0 Gardner. Aniline point, F 185 186 198 186 ASIM D1012-5l. Flash point, TOG, F, 760 mm 133 140 192 164 ASTM D56-52. Color, Saybolt +30 +30 +30 +30 ASTM D15653T.

action. In addition to reducing the polymer formation in the production of vinylcyclohexene from 1,3-butadiene, this diluent permits greatly increased reaction rates, in the order of 2 to 2% times that realized when employing the reaction product, vinylcyclohexene, as the solvent as is conventionally done. The reaction rates which'can be 7 obtained in the process of our invention even exceed those obtained when employing other inert solvents. We have found that when employing the diluent above described which boils in the lower portion of the range specified, namely from about 335 to 410 F., surprisingly high reaction'ratescan be realized. The use of this diluent in the process of our invention for the formation of vinylcyclohexene .by dimerizing 1,3-butadiene enables high The selective dimerization of our invention is carried.

out by mixing the conjugated diene with the diluent above described in a volume ratio of approximately /2 to 3 volumes of diluent per volume of diene. Somewhat less diluent than this can be employed with improved results and although greater amounts of diluent can be used, for economy of reactor capacity it is not advisable. In the manufacture of vinylcyclohexene We prefer to employ about equal volumes or approximately equal weights of diluent and butadiene. p

The reaction mixture is then subjected to 'dime'rizing conditions which are substantially those known and employed in the art. For example, suitable temperatures to effect selective dimerization are in the range "of about 250 to 500 F. and at least suflicient pressure to maintain the reaction mixture in the liquid phase. In preparing vinylcyclohexene by this reaction we prefer to use a temperature between about 300 to 400 F. and a pressure in the range of approximately 100 to 500 pounds per square inch gauge. We have found that, in general, when employing the diluent specified for our invention, higher temperatures can be employed than are normally used with conventional diluents and polymer formation is still maintained at a low level. The reaction time can vary over a broad range, for example from a few (15 or 20) minutes in continuous reactions to several hours in batch processes, as high as 20 hours or more being desirable at times. Normally we prefer operations employing reactor residence times in the order of l to hours. As the reaction proceeds additional diene can be fed to the reactor to maintain the pressure at the desired level. Another approach is to premix the butadiene and diluent, continuously feed the mixture to the reaction zone and withdraw efiluent as the reaction proceeds. Separation of the dimer from the diluent can be effected by any suitable method, fractional distillation being preferred when boiling points dir'ier sufficiently to make this means practicable. Dimers of the 5 and 6 carbon atom dienes will separate less readily from the preferred diluent by tractional distillation and other methods such as fractional crystallization can be employed.

To further describe the advantages and features of our invention the following examples are presented. The reactants and their proportions and other specific conditions are presented as being typical and should not be construed to limit the invention unduly.

EXAMPLE I 1,3-butadiene and highly branched parafi'inic diluent corresponding to diluent A described above were premixed in a volume ratio of 1 to 1 and fed from a weighed bomb to a stainless steel reactor equipped with a mechanical stirrer, heating and cooling coils. The reactor had been purged with nitrogen and the reaction mixture was fed under a nitrogen pressure of 250 pounds per square inch gauge. A similar mixture of butadiene and vinylcyclohexene was prepared and processed in like manner. The results of these runs are reported below in Table 1 showing reactor conditions and yields. Reaction mixture was fed to the reactor to maintain a constant pressure and therefore feed rate is an indication of the rate of reaction of the butadiene.

Table 1 Run 1 2 3 4 Dlluent A Temperature, F 450 400 Pressure, pounds per square inch gauge Dlluent 250 250 Vlnyleyc ohexene 26 Dlluent A Residence Time, hours Feed Rate, grams butadiene/ hour Yield, mol percent based on butadiene consumed:

vinylcyclohexene 8 3 71. 2 78. 7 Polymer l 1 l7. 6 19. 1

EXAMPLE II Mixtures of 1,3-butadiene and solvent were prepared in a 1 to 1 weight ratio and fed as described in Example I to a stainless steel reactor as fast as required to maintain the reactor pressure at 250 pounds per square inch gauge.

Table 2 Dlluent Dlluent Stoddard A B Solvent Reaction Rate, grams butadiene/hour" 865 780 754 The data of Table 2 shows improved reaction rates over an inert naphthenic solvent which is reputed to be inferior to vinylcyclohexene because of increased polymer or gel formation. It is evident therefore from the data presented by these examples that a novel process employing a specific paraflinic solvent is made available for selective dimerization of conjugated dienes at high yields and reaction rates by the practice of our invention.

As will be evident to those skilled in the art, various modifications of this invention can be made, or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope thereof.

We claim:

1. A process for dimerizing lower acyclic dienes which comprises subjecting a lower acyclic conjugated diene to dimerizing conditions of temperature and pressure in the presence of a substantial amount of diluent consisting essentially of material selected from the group consisting of a branched-chain parafiinic hydrocarbon and mixtures of such hydrocarbons substantially free of aromatics and boiling in the range of 270 to 800 F.

2. A process for dimerizing lower acyclic dienes which comprises mixing an acyclic conjugated diene having from 4 to 6, inclusive, carbon atoms per molecule with a diluent consisting essentially of material selected from the group consisting of a branched-chain parafiinic hydrocarbon and mixtures of such hydrocarbons substantially free of aromatics and boiling in the range of about 335 to 500 F. and subjecting said diene in the presence of said diluent to dimerizing reaction conditions including a temperature in the range of about 250 to 500 F. and pressure at least sufficient to maintain the reaction mixture in the liquid phase.

3. A process for producing vinylcyclohexene which comprises dimerizing 1,3-butadiene in the presence of a diluent consisting essentially of material selected from the group consisting of a branched-chain paraflinic hydrocarbon and mixtures of such hydrocarbons substantially free of aromatics and boiling in the range of about 335 to 500 F.

4. A process according to claim 3 wherein said diluent has an initial boiling point of about 350 F. and an end boiling point of about 405 F.

5. In a process for the production of vinylcyclohexene by the dimerization of 1,3-butadiene the improvement which comprises subjecting said butadiene to dimerizing conditions including a temperature in range of 250 to 500 F. and a pressure at least sufiicient to maintain the reaction mixture in the liquid phase for a reaction time between 2 and 40 hours in the presence of a diluent consisting essentially of material selected from the group consisting of a highly branched-chain paraifinic hydrocarbon and mixtures of such hydrocarbons substantially free of aromatics and boiling in the range of about 335 to 500 F., said diluent being present in an amount between about /2 to 3 volumes of diluent per volume of butadiene.

6. In a process for the preparation of vinylcyclohexene by dimerizing l,3-butadiene the improvement which comprises subjecting a reaction mixture of butadiene and diluent consisting essentially of material selected from the group consisting of a highly branched-chain paraffinic hydrocarbon and mixtures of such hydrocarbons substantially free of aromatics and boiling in the range of 350 to 405 F. in a volume ratio between about V2 to 3 volumes of diluent per volume of butadiene to a temperature between about 300 and 450 F., a pressure suflicient to maintain the reaction mixture in the liquid phase and for a time in the range of about /2 to 20 hours.

7. An improved process for preparing vinylcyclohexene which comprises mixing 1,3-butadiene with a paraflinic diluent in a volume ratio of about V2 to 3 volumes of diluent per volume of butadiene, said diluent consisting essentially of material selected from the group consisting of a highly branched-chain paraflinic hydrocarbon and mixtures of such hydrocarbons substantially odorless and free of aromatics and boiling in the range 6 of 350 to 405 F., subjecting the mixture of butadiene and diluent to a temperature between about 300 to 450 F., and suflicient pressure to maintain a liquid phase for from about 1 to 5 hours, and distilling the reaction mixture to recover said vinylcyclohexene.

References Cited in the file of this patent UNITED STATES PATENTS Doumani et al Oct. 15, 1946 Doumani Nov. 26, 1946 OTHER REFERENCES 

1. A PROCESS FOR DIMERIZING LOWER ACYCLIC DIENES WHICH COMPRISES SUBJECTING A LOWER ACYCLIC CONJUGATED DIENE TO DIMERIZING CONDITIONS OF TEMPERATURE AND PRESSURE IN THE PRESENCE OF A SUBSTANTIAL AMOUNT OF DILUENT CONSISTING ESSENTIALLY OF MATERIAL SELECTED FROM THE GROUP CONSISTING OF A BRANCED-CHAIN PARAFFINIC HYDROCARBON AND MIXTURES OF SUCH HYDROCARBONS SUBSTANTIALLY FREE OF AROMATICS AND BOILING IN THE RANGE OF 270 TO 800*F. 